DC-DC converter circuit and inductive load driver using it

ABSTRACT

An inductive load drive device comprising a DC--DC converter circuit which has a coil (L) and switch (Sw) in series with a power source (E) and a capacitor (C) provided in parallel with the switch (Sw). The DC--DC converter produces a high voltage by a procedure in which the switch (Sw) is closed to apply the power source voltage to the coil (L) and then the switch (Sw) is opened to transfer the magnetic energy stored in the coil (L) to the capacitor (C). Using a permanent magnet (Mg), a bias in the direction opposite to that of the magnetic flux induced by the current is applied to the magnetic core of the coil (L) so as to increase the magnetic energy stored in the coil (L). Thus, a DC--DC converter circuit in which a capacitor is efficiently charged through a small-sized coil is realized, and an inductive load drive device having a small size and a light weight is also realized.

TECHNICAL FIELD

The present invention relates to a DC--DC converter circuit and aninductive load driver using this DC--DC converter circuit; inparticular, it relates to an inductive load driver using a DC--DCconverter circuit to ensure a good rise characteristic of the loadcurrent by applying a voltage that is stepped up on commencement ofdrive of the inductive load driver.

BACKGROUND ART

In general, in order to operate an electromagnetic actuator such as asolenoid valve at high speed, it is necessary to achieve rapid rise ofthe exciting current, overcoming the inductance.

The transfer function G(S) of the exciting current I with respect to theapplied voltage E when the internal resistance of the coil is R and itsinductance is L is known to be:

    G(S)=(1/R)·(1/(1+L·S/R))                 (1)

and, as is clear from this equation, the gradient of the rise of currentimmediately after application of voltage E in the condition where I=0 isE/L, while the steady current is E/R; it is known that first-order delayof time-constant L/R is produced.

Consequently, in order to achieve fast operation with a rapid rise incurrent in a coil of fixed R and L, it is necessary to employ a largeapplied voltage E. However, when the applied voltage is increased, thesteady current also becomes larger than necessary, causing heat to begenerated in the coil, which tends to cause burn-out or results inincreased size of the device or waste of energy. Also, in the case ofmachines in for example a moving vehicle that are powered by a batterymounted in the vehicle, the voltage that can be applied is limited, sooften sufficient voltage is not obtained.

In order to solve this problem, a voltage step-up circuit (e.g. aflyback DC--DC converter) for raising the voltage applied to the coiland a current control circuit for controlling the steady current havebeen provided, so as to achieve rapid increase of the current byapplying high voltage on current rise, and preventing increase of thecurrent by more than is necessary by using the current control circuitto suppress the applied voltage when the current reaches a prescribedvalue.

FIG. 31 shows an example of a conventional inductive load driver using aDC--DC converter of the flyback type as voltage step-up circuit. In thisfigure, 1 is a charger circuit comprising a flyback-type DC--DCconverter.

One of the problems in using a flyback-type DC--DC converter as avoltage step-up circuit is the problem of efficiency and increased sizeof the device. Conventionally, a choke coil or transformer were oftenused as the inductance of the charger circuit in order to accumulateenergy, but these suffered from the problem that they increased the sizeof the device and lowered the efficiency of the circuit.

In particular, in applications in which accumulation and discharge ofenergy to the coil is repeated at a high rate, as for example in aflyback type DC--DC converter or voltage step-up chopper, asemiconductor switch was employed as the switching means foraccumulating the energy in the coil. However, the efficiency of thecircuit was adversely affected by losses produced by the voltage drop onclosure of this semiconductor switching means and switching losses inthe opening/closing process. Furthermore, in addition to the volume ofthe ancillary devices needed to dissipate the heat generated by thedevice due to power loss in this semiconductor switching means, and thevolume of the coils or transformer for the accumulation of this energy,the device as a whole tended to become larger and more complicated.

Also, in a DC--DC converter circuit as described above such as iscurrently being used for power supply to electronic devices, the effectson reliability of the device as a whole of ripple of the power sourcecurrent consumed by the circuit present a problem.

The present invention is characterized in that, in a DC--DC convertercircuit using a coil or transformer provided with a magnetic core inwhich a process is repeated whereby energy is introduced into the corefrom a power source and once energy has been accumulated in the core,the energy accumulated in the core is discharged to a load, the energythat is capable of being accumulated in this core is increased bymagnetically biasing the core of the coil for energy accumulation in theopposite direction to the direction in which it is magnetized when theenergy is introduced.

The fact that when energy is accumulated by a coil having a core theenergy that is capable of being accumulated in the core can be increasedby magnetic biasing of this core in the direction opposite to themagnetic field that is generated by the current that is passed when theenergy is accumulated is disclosed in Japanese Patent Kokai PublicationNo. H.2-37705 and Japanese Utility Model Kokai Publication No.Sho.48-49425 etc. However, these all relate to ignition devices forinternal combustion engines and do not solve the various problemsinvolved in applications such as DC--DC converter circuits as describedabove.

Also, biasing the magnetic core of a transformer provided in a DC--DCconverter circuit by means of a DC magnetic field is disclosed inJapanese Utility Model Kokai Publication No. Sho.57-58986, but this isan invention relating to a so-called forward type DC--DC converter: ithas no effect in increasing the energy accumulated on the transformerand so does not solve the problems described above.

Thus, in conventional inductive load drivers, attempting to improve therise characteristic of the inductive load, when using a flyback-typeDC--DC converter, resulted in the problems of increased size andcomplexity of the device.

An object of the present invention is to provide a DC--DC convertercircuit that solves all these problems and which is of small size andlight weight and whose circuit construction is uncomplicated andefficient, and inductive load driver using this DC--DC convertercircuit.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, in a DC--DC converter circuithaving a power source and a coil or transformer provided with a coreconnected to the power source, in which energy is accumulated on thecore by applying the power source voltage to the coil or transformer andthe energy accumulated on the core is then discharged to a load, thisprocess being performed repeatedly, the DC--DC converter circuit of thepresent invention is characterized in that the magnetic energyaccumulated on the coil or transformer is increased by magneticallybiasing the core of the coil or transformer in the opposite direction tothe direction of magnetization induced by the current supplied from thepower source.

Further, in a DC--DC converter circuit comprising the power source, acoil having a core and connected to the power source, switching meansthat opens and closes a closed circuit containing the power source andthe coil, rectifying means whereof one end is connected to the switchingmeans with the object of preventing reverse current, and a capacitorconnected in parallel with the switching means through the rectifyingmeans, in which energy is accumulated on the coil by applying the powersource voltage to the coil by closing the switching means, and theenergy accumulated on the coil is accumulated on the capacitor andoutput through the rectifying means by opening the switching means withdetermined timing that may be determined arbitrarily, it ischaracterized in that the core of the coil is magnetically biased in thedirection opposite to the magnetic field induced by the current suppliedfrom the power source.

Further, in a DC--DC converter circuit comprising the power source, afirst coil having a core and connected to the power source; switchingmeans that opens and closes a closed circuit including the power sourceand the first coil; at least one second coil whose core is common withthe first coil; rectifying means connected to one end of the secondcoils with the object of preventing reverse current; and capacitorsrespectively connected in parallel with the second coils through theserectifying means; wherein, by closing the switching means, the powersource voltage is applied to the first coil, causing energy to beaccumulated on the core of the first coil, and, by opening the switchingmeans with timing that may be determined arbitrarily, the energyaccumulated on the core is accumulated on the respective capacitors bycurrents induced in the second coils through the rectifying means, andis output, it is characterized in that the magnetic energy accumulatedon the first coil is increased by magnetically biasing the core in thedirection opposite to the magnetic field induced by the current suppliedfrom the power source.

Further, in a DC--DC converter circuit comprising the power source, acoil connected to the power source and having a core, switching meansthat opens and closes a closed circuit containing the power source andthe entire winding or a partial winding of the coil, rectifying meansconnected to one end of the entire winding or a partial winding of thecoil with the object of preventing reverse current, and a capacitorconnected in parallel with the entire winding or partial winding of thecoil through this rectifying means, wherein closure of the switchingmeans applies the power source voltage to the entire winding or partialwinding of the coil, thereby accumulating energy on the core of thecoil, and wherein, by opening the switching means with a timing that canbe determined arbitrarily, energy accumulated on the core is accumulatedon at least one of the capacitors as electrical energy induced in theentire winding or partial winding at least one location of the coilthrough the rectifying means, before being output, it is characterizedin that the magnetic energy accumulated in the coil is increased bymagnetically biasing the core in the opposite direction to the magneticfield induced by the current supplied from the power source.

Further, in a DC--DC converter circuit comprising the power source, afirst coil connected to the power source and having a core, switchingmeans that opens and closes a closed circuit containing the power sourceand the first coil, first rectifying means connected to at least one endof the switching means with the object of preventing reverse current, afirst capacitor connected in parallel with the switching means throughthis first rectifying means, a second coil connected to the firstcapacitor, second rectifying means preventing reverse current of thecurrent flowing through the second coil, and a second capacitorconnected to the second coil through this second rectifying means,wherein closure of the switching means applies power source voltage tothe first coil so that energy is accumulated on the core of the coiland, by opening the switching means with a timing that may be determinedarbitrarily, the energy accumulated on the first coil is accumulated onthe first capacitor through the first rectifying means and the energythat is output from the first coil, including the charge on the firstcapacitor is accumulated on the second capacitor through the second coiland second rectifying means before being output, characterized in that,by magnetically biasing the core of the first coil in the oppositedirection to the magnetic field induced by the current supplied from thepower source, the magnetic energy accumulated on the coil is increased.

Further, in a DC--DC converter circuit comprising the power source, afirst coil having a core and connected to the power source, switchingmeans that opens and closes the closed circuit containing the powersource and the first coil, at least one second coil whose core is commonto the first coil, first rectifying means connected to one end of thesecond coil with the object of preventing reverse current, firstcapacitors respectively connected in parallel with the second coilsthrough these first rectifying means, a third coil connected to at leastone of the first capacitors, second rectifying means that preventreverse current of the current flowing through the third coil, and athird capacitor connected to the third coil through these secondrectifying means; wherein, by closing the switching means, the powersource voltage is applied to the first coil, thereby accumulating energyon the core of the first coil; the energy accumulated on the core byopening the switching means with timing that may be determinedarbitrarily is accumulated on the respective first capacitors by meansof the current induced in the second coil through the first rectifyingmeans; and energy output from the second coil including the charge ofthe first capacitor is accumulated on the third capacitor through thethird coil and second rectifying means; it is characterized in that bymagnetically biasing the core in the direction opposite to the magneticfield induced by the current supplied from the power source, themagnetic energy accumulated on the first coil is increased.

Further, in a DC--DC converter circuit comprising the power source, afirst coil connected to the power source and having a core, switchingmeans that opens and closes a closed circuit including the power sourceand the entire winding or a partial winding of the first coil, firstrectifying means connected to one end of the entire winding or partialwinding of the coil with the object of preventing reverse current, firstcapacitors connected in parallel with the entire winding or partialwinding of the coil through these first rectifying means, a second coilconnected to at least one of the first capacitors, second rectifyingmeans preventing reverse current of the current flowing through thesecond coil, and second capacitors connected to the second coil throughthe second rectifying means; wherein closure of the switching meansapplies the power source voltage to the entire winding or partialwinding of the coil, causing energy to be accumulated on the core of thecoil, and wherein the energy accumulated on the core by opening of theswitching means with a timing that can be determined arbitrarily isaccumulated on at least one of the first capacitors as electrical energyinduced in the entire winding or at least one location of the partialwinding of the first coil through the first rectifying means, and theenergy that is output from the first coil, including the charge of thefirst capacitors, through the second coil and second rectifying means,is accumulated on the second capacitors and output; it is characterizedin that the magnetic energy accumulated on the first coil is increasedby magnetically biasing the core of the first coil in the oppositedirection to the magnetic field induced by the current supplied from thepower source.

The magnetic bias may be effected by means of a permanent magnetprovided on the core or by supplying a desired current from aconstant-current source to a biasing coil provided on the core.

Further, it is characterized by the provision of: the power source, theDC--DC converter circuit that generates a voltage higher than the powersource and is connected to the power source, and high voltage switchingmeans for applying to an inductive load the output of the DC--DCconverter circuit.

Further, in an inductive load drive device comprising a power source, aDC--DC converter circuit 1 that is connected to the power source andthat generates a voltage higher than the power source voltage, highvoltage switching means that switches on or off the output of the DC--DCconverter circuit, a logical summation circuit that is capable ofdriving the high voltage switching means in response to any of the atleast one high voltage switch drive signals that it inputs, at least onehigh voltage distributive switching means for connecting the output ofthe high voltage switching means to at least one inductive load, a lowvoltage power source connected to the power source and that outputs avariable output voltage at or below the power source voltage, loadcurrent detecting means that detects load current flowing in theinductive load, at least one analogue constant-current output circuitconnected to the low voltage power source, that inputs a holding currentvalue signal and a load current feedback signal from the load currentdetecting means, and that controls the load current to a value matchingthe holding current value signal, a low voltage power source adjustmentcircuit that inputs the voltage drop amount of output means of thisanalogue constant-current output circuit and that generates a signal tolower the output voltage of the low voltage power source circuit if thisvoltage drop amount exceeds a prescribed value, at least one low voltagedistributive switching means for connecting the output of the analogueconstant-current output circuit to the at least one inductive load, andat least one surge absorption means that absorbs the self-inductionenergy of the load generated when the drive current of the at least oneinductive load is reduced, and a signal processing circuit that inputsat least one load drive signal and, in respect of these respective loaddrive signals, during a prescribed fixed period from a time pointsignifying the commencement of the load drive in question, outputs ahigh voltage switch drive signal for driving the high voltage switchingmeans and a drive signal of the high voltage distributive switchingmeans for connecting the output of the high voltage switching means tothe load that is to be driven, which is determined by the load drivesignal and, during a period for which the load drive signal that isinput signifies continuance of load drive, outputs a prescribed holdingcurrent value signal to the analogue constant-current output circuitand, concurrently, outputs a drive signal of the low voltagedistributive switching means for connecting the output of the analogueconstant-current output circuit to the load that is to be driven, whichis determined in accordance with the load drive signal.

In this invention, the operating point is shifted by applying bias tothe magnetic field of the coil. By this means, the energy density perunit area of the magnetic core can be raised, and the energy accumulatedin the coil can thereby be increased. Consequently, by using acomparatively small coil, a DC--DC converter of small size and highefficiency can be obtained, and, by using such a DC--DC converter, aninductive load driver of high efficiency can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an embodiment of a DC--DC convertercircuit according to the present invention;

FIG. 2 is a diagram showing how the energy density is raised by applyingbias to the core;

FIG. 3 is a circuit diagram showing a specific example of an embodimentof a DC--DC converter circuit according to the present invention shownin FIG. 1;

FIGS. 4(a) and 4(b) are diagrams showing the B-H characteristic of thecore of a coil, and the operating current characteristic in a prior artexample;

FIGS. 5(a) and 5(b) are diagrams showing the B-H characteristic of thecore in the embodiment shown in FIG. 3 and its operating currentcharacteristic;

FIGS. 6(a) and 6(b) are diagrams showing the B-H characteristic of thecore of a coil, and the operating current characteristic when the numberof windings of the coil is halved in a prior art example;

FIG. 7(a) and 7(b) are diagrams showing the B-H characteristic of thecore and operating current characteristic when the magnetic bias isfurther increased in he embodiment shown in FIG. 3;

FIG. 8 is a diagram showing the operating current characteristic of acoil when the number of windings of the coil is reduced by a factor of1/4 in a prior art example;

FIG. 9 is a circuit diagram showing another embodiment of a DC--DCconverter circuit according to the present invention;

FIGS. 10(a), 10(b) and 10(c) are circuit diagrams showing a modificationof the embodiment shown in FIG. 9 of a DC--DC converter circuitaccording to the present invention;

FIG. 11 is a circuit diagram showing another modification of theembodiment shown in FIG. 9 of a DC--DC converter circuit according tothe present invention;

FIGS. 12(a) and 12(b) are circuit diagrams showing yet anotherembodiment of a DC--DC converter circuit according to the presentinvention;

FIG. 13 is a circuit diagram showing a modification of the embodimentshown in FIG. 12 of the DC--DC converter circuit according to thepresent invention;

FIGS. 14(a), 14(b) and 14(c) are circuit diagrams showing yet anotherembodiment of the DC--DC converter circuit according to the presentinvention; FIGS. 15(a) and 15(b) are diagrams showing a prior artexample of a current resonance type DC--DC converter circuit; FIGS.16(a) and 16(b) are diagrams showing yet another embodiment of theDC--DC converter circuit according to the present invention;

FIGS. 17(a) and 17(b) are circuit diagrams showing yet anotherembodiment of the DC--DC converter circuit according to the presentinvention;

FIG. 18 is a circuit diagram showing yet another embodiment of theDC--DC converter circuit according to the present invention;

FIG. 19 is a circuit diagram of an embodiment of an inductive loaddriver using the DC--DC converter circuit according to the presentinvention;

FIG. 20 is a configuration diagram of a means for generating a choppingsignal used in the inductive load drive device shown in FIG. 19;

FIG. 21 is a waveform diagram of various parts of the inductive loaddriver shown in FIG. 19;

FIG. 22 is a waveform diagram of the various parts of an inductive loaddriver shown in FIG. 19;

FIG. 23 is a circuit diagram of another embodiment of the inductive loaddriver using the DC--DC converter circuit according to the presentinvention;

FIG. 24 is a configuration diagram of a signal processing circuit usedin the inductive load driver shown in FIG. 23;

FIG. 25 is a waveform diagram of various parts of the signal processingcircuit shown in FIG. 24;

FIG. 26 is a waveform diagram of a drive signal that is input to thesignal processing circuit shown in FIG. 25;

FIG. 27 is a waveform diagram of a drive signal that is input to thesignal processing circuit shown in FIG. 25;

FIG. 28 is a waveform diagram of a drive signal that is input to thesignal processing circuit shown in FIG. 25;

FIG. 29 is a configuration diagram of an analogue constant-currentcircuit used in an inductive load driver shown in FIG. 23;

FIG. 30 is a configuration diagram of a monitor circuit used in theinductive load driver shown in FIG. 23; and

FIG. 31 is a circuit diagram of a prior art example of a DC--DCconverter circuit.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the DC--DC converter circuit and inductive load driverusing this DC--DC converter circuit according to the present inventionare described below with reference to the drawings.

FIG. I shows a first embodiment of a DC--DC converter circuit accordingto the present invention.

The operation of this circuit will be described with reference to thedrawings. Capacitor C is charged with power source voltage by a powersource E. A closed circuit A is then formed by closing a switch Sw. Atthis point, the charge accumulated on capacitor C is prevented fromflowing back by rectifying means D, and so is held on capacitor C. Thepower source voltage E is also applied to inductance L, therebyincreasing the current of closed circuit A. Energy is accumulated in thecore of inductance L with increase in this current.

Next, when switch Sw is opened, with a timing that can be selected,closed circuit A is released, but, since inductance L acts so as to tryto maintain the current by means of its self-inductance, the circuitcurrent flows through the closed circuit B comprising inductance L,rectifying means D and capacitor C, so that the energy accumulated ininductance L is charged on to capacitor C.

By repetition of this action, capacitor C is gradually charged up tohigh voltage. Reverse flow of the voltage accumulated on capacitor C isprevented by the rectifying means D, so this voltage continues to riseevery time energy is supplied from inductance L, so a voltage higherthan the source voltage can be obtained.

When the voltage of capacitor C exceeds the desired value, this isdetected by means for voltage detection, not shown, and the opening andclosing of switch Sw is stopped; if, during the stoppage of opening andclosing of switch Sw, the value of the voltage gets less than thedesired value, opening and closing of switch Sw is recommended.

In this embodiment, a permanent magnet Mg is used to apply a magneticbias to the core of inductance L for charging capacitor C, this biasbeing applied in the opposite direction to the magnetic field generatedby the current supplied from the power source: more energy can therebybe accumulated by inductance L in a single current passage cycle.

The principle of this will now be described with reference to FIG. 2. Atypical B-H curve of a coil is shown in FIG. 2(a). In order to simplifythis Figure, the magnetic hysteresis characteristic possessed by thecore is omitted. Also, for purposes of explanation, FIG. 2(b) shows asimplified version of this Figure, paying special attention to thesaturation characteristic of the core.

When now a current IL(A) flows in this coil, a magnetomotive force a isapplied by the winding, so that energy Wa is accumulated on the core.

If, in this process, the current IL is increased with the object ofincreasing this accumulated energy Wa, thereby increasing themagnetomotive force a, once the saturation point c of the core isexceeded, further increase of the accumulated energy is undesirable.Furthermore, with saturation of the core of the coil, the current, whichhad hitherto increased according to the relationship IL=E/L·t (where Lis the inductance at magnetic field 0 shown in FIG. 2(b)), due to theabrupt decrease of the inductance, shows an abrupt increase in rate ofcurrent increase per unit time, which may risk causing the destructionof the switching means etc.

Next, the B-H characteristic when magnetic bias is applied in thedirection opposite to the direction of excitation by the current IL ofthe core of this coil is shown in FIG. 2(c).

In FIG. 2(c), when no current is flowing in the coil, due to the biasmagnetic field, the core is in a practically saturated condition in theopposite direction to the magnetic flux that is excited by current IL.When, in this condition, a current IL passes in the coil, energy Wbshown in the Figure is accumulated on the core.

If in this condition the current is increased to the saturation point cof the core, it is clear from the Figure that the energy Wb which isaccumulated is four times the accumulated energy Wa obtained in the casewhere the coil core is not biased.

This relationship will be described in more detail with reference toFIG. 3 to FIG. 6.

In FIG. 3 to FIG. 6, for simplicity of description, real numbers areemployed, and the capacity of the energy storage capacitor is taken asbeing infinitely large i.e. it is viewed as a voltage source. In anactual DC--DC converter circuit, the terminal voltage of the energystorage capacitor fluctuates, but this does not impair the effect of thepresent invention.

FIG. 3 shows a circuit diagram of the DC--DC converter circuit.Capacitor C that is connected in parallel with power source E is afilter capacitor for absorbing ripple of the power source currentconsumed by the circuit.

Now, FIG. 4(a) shows the B-H characteristic when no magnetic bias isapplied to the core of coil L. For convenience, it will be assumed thatthe inductance of this coil L is 10 Mh, and that the core of coil L ismagnetically saturated when a current 10 A is passed through the coil.

The operating current of this DC--DC converter when no magnetic bias isapplied is shown in FIG. 4(b).

When switching means Sw is closed at time point t=0, the coil current ILis:

IL=E/L·t i.e. it increases with a gradient of 1000 A/sec, reaching thesaturation point current 10 A of the coil in 10 msec.

At this point, the energy supplied to the coil from the power source is1/2·(10 A)·(10 V)·(10 msec)=0.5 J.

Next, when switching means Sw is released at this time point, thecircuit becomes a closed circuit consisting of power source E, coil L,rectifying means D, and output-side voltage source Ce.

If now the voltage of the output-side voltage source Ce is taken as 110V, and it is assumed that there is no voltage drop at rectifying meansD, a voltage of 100 V of opposite polarity to the direction of thiscurrent flow will be applied to coil L, so

    IL=IL(MAX)-100/L·t

i.e. it decreases at a rate of 10000 A/sec.

Since IL (MAX)=10 Ma, the coil current after 1 msec is 0 A. Thus, inthis process, energy

1/2·(10 A)·(100 V)·(1 msec)=0.5 J is discharged on the output side. Infact energy of {1/2·(10 A)·(10 V) ·(1 msec)} is present, transmitteddirectly to the output side from the power source at this point;however, in this connection we are concerned with the accumulation ofenergy by the coil and, since the energy term that is directlytransmitted to the output side from this power source does not directlyrelate to the essence of the present invention, description concerningthis energy is omitted; this treatment will be continued in thedescription below.

The time required for the accumulation and discharge of this energy isthe sum of the time ta=10 msec for the accumulation of energy of thecoil and the time tb=1 msec for the discharge of energy from the coili.e. 11 msec. This circuit is therefore capable of supplying energy of0.5 J to the output from the power source in a period of 11 msec.

The case where the same coil is employed but its core is magneticallybiased will now be described.

FIG. 5(a) shows the characteristic of this biased coil.

When a permanent magnet is used to apply bias, there would normally bean increase in the value of the inductance and the saturation magneticflux amount, because of the addition of the magnetic body constituted bythe permanent magnet to the core of the coil; however, in this case,these effects are either absent or can be described in terms of the casewhere magnetic bias is applied by passing a constant current to a secondwinding, not shown.

In other words, in this case, the inductance does not change and thesaturation characteristic of the core is also unchanged, so, as shown inFIG. 5(a), the characteristic of this coil simply consists of acharacteristic obtained by shifting the characteristic of FIG. 4(a) inparallel to the right.

When switching means Sw is then closed, power source E is applied tocoil L as described above, increasing the coil current IL by 1000 A/sec.When this coil current IL is increased to the saturation point of thecore as described above, IL (MAX) at this point is 20 A, and the timerequired for the increase in current is then 20 msec. This process isshown in FIG. 5(b). Also, the energy accumulated on the coil during thisprocess is

    1/2·(20 A)·(10 V)·(20 msec)=2.0 J

which is four times the energy accumulated on the coil if bias is notapplied as described above.

When, at this time point, switching means Sw is opened, just asdescribed above, the coil current decreases at the rate 10000 A/sec,becoming 0 A after 2 msec. During this period, the energy discharged bythis coil is

    1/2·(20 A)·(100 V)·(2 msec)=2.0 J

and, since, in FIG. 5(b), ta=20 msec and tb=2 msec, energy of 2.0 J canbe supplied on the output side from the power source in 22 msec.

Thus, compared with the case described above where an unbiased coil isemployed the amount of energy passing through the circuit per unit timeis doubled.

What is important in a DC--DC converter circuit is not the amount ofenergy accumulated in the coil per cycle, but rather the amount ofenergy that can be handled by the circuit in unit time. Furtherexplanation concerning this point will now be given.

Let us now consider the objective to be increasing the amount of passageof energy per unit time of DC--DC converter circuits having cores ofidentical volume. A method of solving this problem which has been knownfor a long time is to reduce the value of the inductance.

FIG. 6(a) shows an inductance characteristic based on this principle. Inthis example, a coil is assumed wherein the number of windings wound onthe core is reduced by half from that of the preceding example. If thisis done, the current that can be passed at the saturation point of thecore is doubled and the inductance is reduced by a factor of 1/4.

The operation will now be described using the circuit of FIG. 3 in whichsuch a coil is employed. When switching means Sw is closed at time t=0,the power source voltage E is applied to coil L, causing the coilcurrent to increase in accordance with IL=E/L·t. Since the inductance ofcoil L is 1/4 of the above value i.e. 2.5 Mh, this current increases atthe rate 4000 Ma/sec. Furthermore, the coil current at the saturationpoint of the core of this coil is twice what it was in the aboveexample, i.e. it is 20 A. The time required for excitation up tosaturation of this coil is therefore

    (20 A)/(4000 Ma/sec)=5 msec.

The energy accumulated on the coil during this period is

    1/2·(20 A)·(10 V)·(50 msec)=0.5 J

Also, since the value of the inductance is 2.5 Mh, the rate of decreaseof the coil current at this time point when switching means Sw is openedbecomes 40000 A/sec, so the current of 20 A becomes 0 A after 0.5 msec.Also, the energy hat coil L supplies to the output during this period is

    1/2·(20 A)·(100 V)·(0.5 msec)=0.5 J

As shown in FIG. 6(b), this means that the time required to accumulatethe energy on this coil is ta=5 msec and the time required to dischargethis at the output is tb=0.5 msec, making a total of 5.5 msec requiredby the circuit for transmission of energy of 0.5 J from the power sourceto the load. By repeating this operation four times, the same amount ofenergy in the same amount of time as in the case where the biased coildescribed above was used can be supplied from the power source to theload.

This means that the amount of energy transmitted per unit time using thesame core can be increased. In applications such as DC--DC converters,it is desirable that as much energy as possible should be transmittedper unit time.

However, if, using such an unbiased coil, the value of the inductance isdecreased, with the same maximum current as in the case of using abiased coil, switching means Sw employed in the circuit of FIG. 3 mustbe turned off with a frequency that is four times greater; particularlyif a small core is employed in order to reduce the overall size,switching loss at this switching means Sw becomes non-negligible. Themethod according to the present invention, wherein a biased coil isemployed is thus superior in that it results in lower switching lossthan a method in which the value of the inductance is decreased.

In the example of FIG. 5, in biasing the core of the oil, the biasingvalue is selected at which the core is magnetically saturated by itselfin exactly the opposite direction in the condition where no coil currentis being passed. What happens if this magnetic biasing value is madeeven deeper is described with reference to FIG. 7. FIG. 7(a) shows theB-H characteristic in this case.

The coil is of 10 Mh just as in the case of the example of FIG. 4 andFIG. 5; for the magnetic biasing value, a value is selected such thatmagnetic saturation is achieved in the opposite direction by a coilcurrent of 10 A. The behavior of such a coil will now be described whenthe circuit of FIG. 3 is adopted for the coil L.

If now switching means Sw is closed, power source voltage is applied tocoil L, but, since the core is saturated in the reverse direction whilstthe current is still small, the value of the inductance is very smalland as a result the coil current increases rapidly, reaching 10 Apractically instantaneously. Let the value of the current under theseconditions be taken as the minimum current value IL (MIN) for which thecoil L can take the prescribed inductance value. Thereafter, the coilcurrent increases in accordance with IL=IL (MIN)+E/L·t, until it reachesthe saturation point in the direction of the magnetic field produced bythe current.

Since the volume of the core of this coil and the number of windings ofthe coil are the same as in the case of the example of FIG. 4 and FIG.5, the coil current at the saturation point is 30 A. The time fromclosure of switching means Sw until the current reaches this saturationpoint is (30 A-10 A) / (1000 A/sec)=20 msec.

Furthermore, the energy supplied during this period from the powersource to the coil L is 1/2·(10 A+30 A)·(10 V)·(20 msec)=4.0 J.

In the process in which switching means Sw is then opened from thiscondition so that the energy accumulated in coil L is discharged at theoutput, the voltage in the opposite direction applied to coil L byoutput-side voltage source Ce is 100 V, and the rate of decrease of thecoil current of this coil L is 10000 A/sec. The initial current of 30 Atherefore drops to 10 A after 2 msec. When the current value gets below10 A, as described above, the core of coil L is magnetically saturatedin the reverse direction, so the coil current is immediately decreasedto 0 A. In this process, the energy discharged by coil L on the outputside is

    1/2·(30 A+10 A)·(100 V)·(2 msec)=4.0 J.

The way in which the current changes during this period is shown in FIG.7(b).

After switching means Sw is closed at t=0, the time required for energyof 4.0 J to be accumulated in coil L is ta=20 msec, and the timerequired for the accumulated energy to be discharged is tb=2 msec i.e.the circuit can transmit energy of 4.0 J from the power source to theoutput in 22 msec.

Attempting to achieve this with an unbiased coil, if an identical corewere used, would mean that a coil of 1/4 the number of windings wouldneed to be employed. Its inductance characteristic would be as shown inFIG. 8.

Since its number of windings is 1/4, the current at saturation point ofthis core would be 40 A and its inductance would be 1/16 i.e. 0.625 Mh.The operation obtained when such a coil was applied to the circuit ofFIG. 3 will now be described.

If now the switching means Sw is closed at t=0, the coil current risesin accordance with IL=E/L·t with a rate of increase of 16000 A/sec.Since the current value at the saturation point of this coil is then 40A, the time required to reach this is 40 A/16000 A/sec=2.5 msec. In thisprocess, the energy supplied from the power source to the coil is1/2·(40 A)·(10 V)·(2.5 msec)=0.5 J.

Also, if we assume that the energy accumulated on this coil isdischarged at the output side by opening switch Sw at this time point,the rate of decrease of the coil current during this process is 160000A/sec and the discharge time is 0.25 msec. Thus the energy discharged atthe output side during this period is 1/2·(40 A)·(100 V)·(0.25 msec)=0.5J.

Thus, the circuit was able to transmit from the power source to theoutput side energy of 0.5 J in a period of 2.75 msec. Thus, by repeatingsuch accumulation of energy on to the coil and discharge at the outputeight times, the same amount of energy can be transmitted to the outputside in the same time, with the same core volume as when a biased coilis employed. However, when this magnetically unbiased coil is employed,switching means Sw has to cut off a current of 40 A eight times in orderto obtain the same rate of energy transmission per unit time.

Thus it can be seen that, by biasing the core of the coil, the benefitis obtained that the capacity of the switching means can be reduced to3/4 and its switching frequency can be reduced to 1/8.

In the above, for simplicity, the description of many of the structuralelements has been idealized or simplified, but even in an actualapplication circuit, in a DC--DC converter circuit wherein the core ofthe coil is thus biased magnetically in the opposite direction to thedirection of magnetization produced by the current supplied from thepower source, and energy is accumulated thereon, it is found that, forthe same core volume, increasing the amount of this bias makes itpossible to lower the switching frequency of the switching means and tolower the capacity of the switching means itself.

The overall benefits that can be achieved are therefore: reduction ofthe current passed through the switching means and reduction of theenergy loss resulting from switching, and, because of these, increasedefficiency, simplification of the heat dissipation structure, increasedlife of the switching means and very considerable reduction in theoverall size of the device.

Also, if a deep reverse bias of the coil core is employed, as shown inFIG. 7(b), that part of the current flowing in this coil that is belowIL(MIN) shows a very rapid decrease/increase, so it can easily beabsorbed by a filter capacitor provided at the power source input unitof the circuit; thus, the power source current ripple that is inevitablygenerated in a flyback-type converter can be reduced in the DC--DCconverter circuit of the present invention.

The circuit of a second embodiment of a DC--DC converter circuitaccording to the present invention is shown in FIG. 9.

The basic principle of this embodiment is the same as the firstembodiment, but a multi-winding transformer T is employed instead of thesingle coil of the first embodiment. In this transformer T also, bias isapplied in the opposite direction to the direction of the magnetic fluxgenerated by the passage of the current, using for this purpose apermanent magnet Mg, in order to raise the energy density per unit areaof the core. In this way, a small-size light-weight charger unit can beimplemented, since a smaller transformer can be employed to implement acharger of equivalent performance.

The operation of this circuit will now be described with reference toFIG. 9.

Closed circuit A is formed by closing switch Sw. The energy suppliedfrom the power source is accumulated on primary coil L1 of multi-windingtransformer T. When switch Sw is opened, the energy accumulated inprimary coil L1 shifts to secondary coil L2, with the result that acurrent flows in closed circuit B and capacitor C is charged up. Moreenergy can be accumulated on capacitor C by repeating thisopening/closure operation of switch Sw.

The circuit of this embodiment has the following further advantages.

1) The impedance can be changed on the primary side and secondary side.

That is, by employing a larger number of windings on the primary side oftransformer T, as in FIG. 10(a), and a smaller number of windings on thesecondary side, the impedance on the secondary side can be made lower.The capacitor C provided on the secondary side can thereby be charged upwith low voltage.

Also, if, as shown in FIG. 10(b), the number of windings on the primaryside is made fewer while the number of windings on the secondary side ismade larger, the impedance on the secondary side can be made higher.Capacitor C provided on the secondary side can thereby be charged upwith high voltage. Also, in this case, if the charging voltage ofcapacitor C is taken as being Vc and the windings ratio of thetransformer is r=n2/n1 (where n1 and n2 are respectively the number ofwindings of primary coil L1 and secondary coil L2), the withstandvoltage of switch Sw can be made lower in the ratio Vc/r.

2) Electrical isolation can be achieved between the primary andsecondary side.

That is, electrical isolation can be achieved since the earths of theprimary side and secondary side can be separated as shown in FIG. 10(c).

Yet a further embodiment using a transformer is shown in FIG. 11.

This embodiment is a DC--DC converter circuit wherein there are provideda first winding L1 connected to the power source and two secondarywindings L2-1 and L2-2 sharing a core with this first winding L1.Secondary windings L2-1 and L2-2 are respectively provided with energyaccumulation capacitors C1, C2 for output and rectifying means D1, D2 toprevent reverse current.

After first accumulating energy in the magnetically biased core bypassing current to winding L1 by closing switching means Sw, whenswitching means Sw is opened, respective electromotive forces arecreated in secondary windings L2-1 and L2-2 by the energy accumulated inthe core.

The number of windings of secondary windings L2-1 and L2-2 and theelectromotive forces generated therein are proportional; if the twoterminal voltages of output capacitors C1 and C2 are lower than theelectromotive forces of these secondary windings L2-1 and L2-2, currentflows to the circuit having the lower output capacitor. By this means,using a plurality of secondary windings, by setting the ratio of thenumber of windings of these, a plurality of power sources of differentvoltage can be obtained simultaneously. Furthermore, of the plurality ofoutput circuits, the energy supplied from the power source isconcentrated on the circuit where energy is discharged to load, so thatthe output voltage balance is automatically maintained.

FIG. 12 shows the circuit of another embodiment of a DC--DC convertercircuit according to the present invention.

The basic principles of this embodiment are the same as those of thefirst and second embodiments, but a single-winding transformer Ts isemployed instead of the single coil of the first embodiment. In thistransformer Ts, bias in the reverse direction to the direction of themagnetic flux generated by the passage of current is applied by apermanent magnet Mg, in order to raise the energy density per unit areaof the core. In this way, a smaller transformer can be employed toimplement a charger of equivalent capacity, so a charger unit of smallersize and lighter weight can be achieved.

The operation of this circuit is described below with reference to FIG.12.

Closed circuit A is formed by closing switch Sw. The energy suppliedfrom power source E is accumulated in coil L of single-windingtransformer Ts. When switch Sw is opened, closed circuit B isconstituted, and the energy stored in core L shifts to portion L2 of thecoil, so that current flows in closed circuit B, charging capacitor C.Repetition of this opening/closing action of switch Sw enables moreenergy to be accumulated on capacitor C.

Also, with this circuit, as shown in FIG. 12, just as in the case of thecircuit of the second embodiment, there is the advantage that theimpedance on the primary side and the secondary side can be varied.

FIG. 13 shows yet a further embodiment of a DC--DC converter circuitaccording to the present invention, using a single-winding transformer.

In this embodiment, using a portion of winding L of single-windingtransformer Ts, a closed circuit is formed by the power source andswitching means Sw, as a result of which energy is accumulated on themagnetic core of magnetically biased transformer Ts; switching means Swis then opened, and the accumulated energy is accumulated on energyaccumulating capacitors C1, C2 by rectifying means D1, D2 for reversecurrent prevention, that are connected at a plurality of locations ofwinding L of single-winding transformer Ts, prior to being output.

In this example, just as in the case of the DC--DC converter circuitusing a transformer in which a plurality of secondary windings wereprovided as described above, a plurality of outputs of different voltagecan be output simultaneously.

In the embodiments described above, a permanent magnet Mg was employedas the method of applying bias. Obviously the same effect could beobtained by using an electromagnet Me instead of this. Such an exampleis shown in FIG. 14. FIG. 14(a) is an example using a single coil; FIG.14(b) is an example using a multi-winding transformer; and FIG. 14(c) isan example using a single-winding transformer.

Yet a further embodiment of the DC--DC converter circuit of the presentinvention is shown in FIG. 16.

By using a magnetic bias, as described above, the frequency ofopening/closing of the switching means can be greatly decreased, for thesame core volume, compared with the conventional circuit using a coil inwhich magnetic biasing is not employed; however, for a DC--DC convertercircuit, the reduction in loss of the switching means during switchingis also important.

FIG. 15(a) shows a prior art example of a DC--DC converter circuitanswering this objective. An energy accumulating coil L1 is connected toa power source E and this is close-circuited by switching means Sw,supplying current to coil L1, with the result that energy is accumulatedin the core of coil L1. Switching means Sw is then opened, with a timingthat may be selected arbitrarily. The energy accumulated on coil L1thereby charges capacitor C1 through rectifying means D1. When thisswitching means Sw is opened, charge is not accumulated on capacitor C1,so, even when switching means Sw is opened, voltage is not generated atthe contacts of switching means Sw. The switching loss of switchingmeans Sw is therefore greatly reduced.

The terminal voltage of capacitor C1 subsequently rises with chargingfrom coil L1 until the terminal voltage of capacitor C2 is exceeded.When this happens, current charging up capacitor C2 flows through theseries circuit consisting of capacitor C1, rectifying means D2 andsecond coil L2.

Soon, coil L1 completes the discharge of this accumulated energy, andthe current supplied to capacitor C1 through rectifying means D1 isdecreased. However, the circuit is designed such that the decrease ofcurrent flowing through coil L2 occurs later than this, so that thecharge of capacitor C1 is gradually absorbed on the output side by theself-inductive effect of coil L2, with the result that capacitor C1loses its accumulated charge.

Rectifying means D3 is provided if required, so that, when the chargeaccumulated by capacitor C1 is lost, current IL2 is bypassed andback-voltage is prevented from being applied to switching means Sw.

Such a circuit is operated as a series resonance circuit of capacitor C1and coil L2, so it is usually called a current resonance circuit. Theresonance period of the resonance circuit consisting of capacitor C2 andcoil L2 must be set such that the charge of capacitor C1 becomes zeroafter the current supplied from coil L1 has disappeared.

FIG. 15(b) shows the current waveform at various locations when thissetting is insufficient. Specifically, even if the resonance current IL2produced by coil L2 and capacitor C1 is zero, if IL1 is still present,the voltage between the two terminals of capacitor C1 may again rise,resulting in a residual voltage Rvc1. If this Rvc1 is higher than thevoltage of capacitor C2, a current IL2 is again generated. However, ifRvc1 does not reach the level of the voltage of capacitor C2, thisvoltage is left unmodified at the two terminals of capacitor C1, and isa factor causing switching loss when switching means Sw is again cut offin the next cycle.

FIG. 16(a) shows an example of a DC--DC converter circuit of the currentresonance type circuit configuration, when magnetic bias is applied tocoil Li in accordance with the present invention, and FIG. 16(b) showsthe current waveform that is then obtained.

In this case, by making the magnetic bias of energy accumulating coil L1sufficiently deep, the current that is supplied from coil L1 tocapacitor C1 can be made to change rapidly to OA from a value that isamply sufficient. By this means, the current of coil L1 can be broughtto 0 while there is still a sufficiently large current in coil L2, so atime margin tm is produced as shown in FIG. 16(b) and the benefit ofsuppression of the production of Rvc1 is obtained. Of course, the otherbenefits of the present invention such as reduction of capacity of theswitching means, reduction of input current ripple, reduction ofswitching frequency and reduction in size of the coil are stillobtained.

FIG. 17(a) is a circuit diagram of a current resonance type DC--DCconverter according to the present invention constituted by atransformer having primary and secondary windings sharing a core. Itsbasic operation is the same as in the case of the single coil describedabove. However, if, as shown in FIG. 17(b), it is sought to obtain aplurality of voltages by using a plurality of secondary windings, aresonance circuit for reducing switching loss of switching means Sw maybe provided in any one of the plurality of secondary windings. A designcondition is that the charge of capacitor C1 that is provided forresonance must be eliminated when switching means Sw is open. Also, itis necessary to take care that the other outputs that are concurrentlyprovided have the values obtained by converting the maximum chargingvoltage of capacitor C1 using the turns ratios of the respectivesecondary windings.

FIG. 18 is a circuit diagram of a current resonance type DC--DCconverter according to the present invention constructed using asingle-winding transformer. The DC--DC converter action and resonanceoperation are the same as already described with reference to amulti-winding transformer.

FIG. 19 shows an example of an inductive load drive device using aDC--DC converter circuit according to the present invention as describedabove.

In this circuit, the portion enclosed by dotted lines and indicated byChg is the DC--DC converter circuit of the present invention. ThisDC--DC converter circuit Chg comprises means for detecting current Ctconnected to the power source E, an energy accumulating coil L whosecore is magnetically biased, a first switching means Tr1 that opens andcloses a circuit containing power source E, means for detecting currentCt and energy accumulation coil L, rectifying means D whose anode isconnected to the point of connection of this first switching means Tr1and energy accumulating coil L, an output energy accumulation capacitorC that is connected to the cathode of rectifying means D and to theother terminal of first switching means Tr1, means for voltage detectionHvs that detects the charging voltage of this output energy accumulatingcapacitor C, and means for generating a chopping signal Chp that inputsthe output of means for detecting current Ct and means for voltagedetection Hvs and generates a signal that switches first switching meansTr1 on and off.

This inductive load drive device inputs a drive signal Drv specifyingthe drive of the inductive load; it is connected in parallel with loadZl and second switching means Tr2 that applies to inductive load Zl theoutput of the DC--DC converter and is switched by this drive signal Drv;there is provided a flywheel-current rectifying means (flywheel diode)FD that passes the flywheel current generated by self-inductance of thisload ZL when the current of inductive load ZL is cut off or reduced.

FIG. 20 shows the configuration of means for generating a choppingsignal Chp.

Means for generating a chopping signal Chp comprises internal referencevoltage E1, comparator Comp, means for inverting Th having a hysteresischaracteristic that inputs the signal of means for detecting current Ct,and an AND circuit that supplies to a first switching means Tr1 thelogical product obtained by inputting the output of comparator Comp andthe output of means for inverting Th.

Next, the operation of this DC--DC converter and the various waveformsshown in FIG. 21 and FIG. 22 will be described.

It is assumed that the output of comparator Comp is normally "1"(actuated condition).

At t=0, first switching means Tr1 is closed, and coil current I1 is inthe course of rising. Eventually, coil current I1 reaches a thresholdvalue on the cut-off side of means for inverting Th having a hysteresischaracteristic. This cut-off side threshold value is set to the currentobtaining when sufficient energy has been accumulated on energyaccumulating coil L.

When the coil current I1 exceeds this threshold value, the output ofmeans for inverting Th is cut off, and, concurrently, first switchingmeans Tr1 is also cut off (open-circuited). By this means, the currentI1 of energy accumulating coil L charges the output energy accumulatingcapacitor C through rectifying means D. Current I1 of energyaccumulating coil L is decreased by the discharge of energy to capacitorC until it reaches the power-on side threshold value of means forinverting Th; when this happens, first switching means Tr1 is againclosed. By repetition of these operations, the voltage Vc between thetwo terminals of output energy accumulating capacitor C progressivelyincreases.

The voltage Vc across the two terminals of capacitor C is subjected tovoltage division so as to enable subsequent processing, if necessary, bymeans for voltage detection Hvs, or, if this is not necessary, isdirectly supplied to be compared with reference voltage E1 within meansfor generating a chopping signal Chp. If the voltage Vc across bothterminals of capacitor C, or the value obtained by subjecting this tovoltage division, exceeds reference voltage E1, the output of comparatorComp is cut off, and first switching means Tr1 also holds its cut-off(open) condition.

As shown in FIG. 22, the voltage Vc across both terminals of capacitor Ccorresponding to reference voltage E1 exceeds power source voltage E ofthe circuit, so this voltage is held by reverse-flow preventionrectifying means D.

When, in this condition, load drive signal Drv is input, secondswitching means Tr2 is closed, and the voltage Vc across both terminalsof output energy accumulating capacitor C is applied to inductive loadZL. Load current Iz1 abruptly rises due to the voltage Vc exceeding thepower source voltage E accumulated on this capacitor C. The speed ofcurrent rise and maximum current value at this point are determined bythe impedance of load ZL, the capacitance of capacitor C and the voltageVc across both its terminals; the circuit constants and the magnitude ofthe reference voltage E1 in the means for generating a chopping signalChp, and the voltage division ratio in means for voltage detection Hvsare set such that the desired load current is obtained.

When capacitor C discharges this accumulated energy to load ZL, thevoltage Vc across its terminals decreases. This process is monitored asthe behavior of the resonance circuit of capacitor C and the inductancecomponent of load ZL; eventually the charge of capacitor C disappearsand the voltage Vc across its two terminals becomes 0V. The load currentIz1 is maintained by the self-inductance effect of load ZL, but, since,in this process, the flywheel current rectifying means FD conducts, theload current Iz1 freewheels through the freewheel path constituted byload ZL and flywheel current rectifying means FD, being graduallyreduced by dispersion of its energy in the form of heat by the resistivecomponent of load ZL.

On the other hand, as a result of the decrease of voltage Vc across bothterminals of capacitor C, the output of comparator Comp in means forgenerating a chopping signal Chp is activated, and, as a result, theprocess is repeated in which first switching means Tr1 is again closed,passage of current in energy accumulation coil L is commenced, coilpassage current IL is increased, and first switching means Tr1 isthereby open-circuited by the action of means for inverting Th having ahysteresis characteristic, followed by discharge of the energyaccumulated on the coil to capacitor C. However, at this time point,second switching means Tr2 is closed, so the energy discharged from thecoil is temporarily accumulated in capacitor C, then averaged andsupplied to load ZL.

By this series of operations, a fixed current matching the energysupplied from the coil is supplied to load ZL. When this process isobserved from the time point where the free-wheeling of the load currentIz1 after its initial rapid rise has been completed, it corresponds tozone A in FIG. 22.

Next, when load drive signal Drv terminates after the passage of thedesired load drive time, allowing the second switching means to open,the load current Iz1 decreases to 0A whilst freewheeling throughflywheel-current rectifying means FD. In this way, a voltage exceedingthe power source voltage E is again accumulated on output energyaccumulation capacitor C.

In this way, by using this circuit, by introducing a large amount ofenergy into an inductive load ZL such as for example an electromagneticvalve in the initial period of its operation, opening of the valve canbe advanced, and the value of the load current Iz1 can be reduced to thevalue at which the open condition of the electromagnetic valve ismaintained: in this way, evolution of heat from the load ZL can be keptat a low level. Also, by employing a DC--DC converter wherein the coreof the energy accumulation coil according to the present invention ismagnetically biased as the DC--DC converter circuit used in thiscircuit, production advantages such as miniaturization of the device,improved efficiency, and lower manufacturing costs can be obtained.

FIG. 23 shows a further embodiment of an inductive load drive deviceaccording to the present invention.

This device is constructed so as to be capable of driving four inductiveloads ZL1 to ZL4. The device comprises a DC--DC converter circuit 1having a power source Vb and an energy accumulating coil that isconnected to power source Vb and whose core is magnetically biased, forgenerating a voltage higher power source Vb; high voltage switchingmeans 3 that switch the output of this DC--DC converter circuit 1 on oroff; an OR circuit 15 capable of driving high voltage switching means 3in response to one or other of one or more high voltage switch drivesignals that are input; one or more high voltage distributive switchingmeans 8-1 to 8-4 for connection of the output of high voltage switchingmeans 3 to one or more inductive loads ZL1 to ZL4; a low voltage powersource circuit 5 connected to power source Vp and having a variableoutput voltage of less than the power source voltage; one or moreanalogue constant-current output circuits 4-1, 4-2 connected to this lowvoltage power source circuit 5 and that inputs a holding current signaland a load current feedback signal from load current detecting means10-1, 10-2, and that controls load current to a value matching the holdcurrent; low voltage power source regulating circuits 4-1-1, 4-2-1 thatinput the voltage drops of the output means of these analogueconstant-current output circuits 4-1, 4-2 and that, when the voltagedrops exceed prescribed values generate signals to lower the outputvoltage of low voltage power source circuit 5; at least one surgeabsorption snubber circuits 16-1, 16-2 that absorb the self-inductionenergy of inductive loads ZL1 to ZL4 generated when the drive currentsof the one or more inductive loads ZL1 to ZL4 are reduced; and signalprocessing circuits 2-1 to 2-4 for inputting at least one load drivesignal and outputting a high voltage switch drive signal for drivinghigh voltage switching means 3 for a prescribed fixed time from the timepoint signified by this load drive signal with respect to the variousload drive signals, a drive signal of high voltage distributiveswitching means 8-1 to 8-3 for connection of the output of high voltageswitching means 3 to loads ZL1 to ZL4 to be driven, which are determinedby the load drive signal, and a prescribed holding current value signalto analogue constant-current output circuits 4-1, 4-2 during the periodin which the input load drive signals are indicated as continuing loaddrive, and, simultaneously, for outputting drive signals of low voltagedistributive switching means 6-1 to 6-4 for connecting the output ofanalogue constant-current output circuits 4-1, 4-2 to the load to bedriven determined by the load drive signal, and for outputting adrive-completed signal when termination of the load ZL1 to ZL4 drive isindicated by the input load drive signal.

The operation of this circuit will now be described with reference toFIG. 23.

This drive circuit supplies current to inductive loads ZL1 to ZL4 inaccordance with a drive signal Sig designating drive of inductive loadZL1 to ZL4; drive signal Sig is sent from an ECU (electronic controlunit), not shown, as needed. Examples are: with the object of opening orclosing a hydraulic electromagnetic valve for controlling the actuatorof a hydraulic machine or the like, or with the object of opening orclosing the valve of an electromagnetic injector supplying fuel to anengine, or with the object of opening or closing an electromagneticvalve that controls liquid pressure or gas pressure, or with the objectof exciting/demagnetizing the drive phase of a stepping motor device.

In for example the case of a device where the load is for example anelectromagnetic valve, the characteristic required for the control wouldbe such that: high voltage is applied to the load in the initial periodof drive commencement of the inductive load so as to advance thecommencement of actuation of the load by rapidly increasing the loadcurrent, and, in the step in which the valve is held after the valveopening action has been completed, generation of heat by the load issuppressed by reducing the current value to the value necessary to holdthe load current in the valve-open condition, and, when the load drivehas been completed, that the residual energy of the load is rapidlyeliminated, so that the valve can be rapidly closed.

Also, in the case where the load is a stepping motor device, forexample, the characteristic demanded would be such that, at thecommencement of excitation of the drive phase, a large amount of energyis rapidly introduced into the coil forming the phase so as toaccelerate the movement of the rotor; when the rotor has reached a fixedposition with respect to the pole, the current is decreased so thatgeneration of heat in the coil can be suppressed, and, when excitationshifts from this phase to the next phase, the energy (excitationcurrent) of this phase is rapidly decreased so as to suppress generationof force on the rotor opposing the force with which it is attracted tothe next phase.

Further details of the construction of signal processing circuit 2 areshown in FIG. 24 and the waveforms of the various parts of signalprocessing circuit 2 are shown in FIG. 25.

In FIG. 23, there are provided four of these signal processing circuits2, corresponding to the number of loads ZL1 to ZL4.

Signal processing circuit 2 inputs a drive signal Sig; a monostablemultivibrator 21 is actuated by this inverted drive signal NSig.Monostable multivibrator 21 is operated by the leading edge of inverteddrive signal Nsig, to output a high voltage switch signal Vhon having afixed period Tp, and a high voltage distribution switch drive signalIpsel. If required, it could also output analogue voltage signal Ihrefobtained by voltage division of inverted drive signal Nsig. Analoguevoltage Ihref designates the holding current value in the steady drivecondition of the load. Also, a logic signal corresponding to inverteddrive signal Nsig itself is output as low voltage distribution switchdrive signal Ihsvl. Furthermore, a signal obtained by differentiatingdrive signal Sig is also output as drive completion signal Irsel.

FIG. 26 to FIG. 28 show examples of drive signal that are input to thiscircuit. The drive signals are respectively independently andsuccessively input from Sig1 to Sig4 in FIG. 26. This corresponds forexample to the drive sequence of an injector device in which fuel issequentially supplied to a four-cylinder engine device. Also, regardingthe arrangement of the drive signals Sig1 to Sig4 in FIG. 28, this issuch that the next signal is input simultaneously with the determinationof the respective immediately previous signal. This corresponds forexample to the excitation sequence of drive phases in a four-phasestepping motor device. Further, in FIG. 28, respective drive signals maybe input overlapping by a half-period with the respective immediatelypreceding signal. In this case, Sig1 and Sig3 on the one hand and Sig2and Sig4 on the other are respectively of inverse phase; for exampleoutput channels 1 and 3 on the one hand and 2 and 4 on the otherrespectively correspond to the operating sequences in the alternatelyopened/closed valves of a pair of electromagnetic valves for adouble-shaft hydraulic circuit. This circuit has the benefit that it canbe employed in a wide range of applications since it permits the mutualrelationship of the respective input signals in this way, up to thehalf-period overlap of FIG. 28.

When power source Vb is supplied to the circuit in FIG. 23, the DC--DCconverter circuit 1 for high voltage generation commences the chargingof high voltage, exceeding the power source voltage, accumulation anddischarge of energy with respect to this energy accumulation capacitorbeing repeated until this reaches the prescribed voltage.

Thereupon, when drive signal Sig1 is input, high voltage switch drivesignal Vhonl described above is output from signal processing circuit2-1 and high voltage switching means 3 is thereby closed. Simultaneouslywith this, the high voltage distribution signal drive signal Ipsel1described above is output, and high voltage means for distribution 8-1is also selectively closed. The high voltage obtained by DC--DCconverter circuit 1 is thereby applied to inductive load ZL1 rapidlyincreasing the load current of inductive load ZL1. At this point,holding current value signal Ihref1 is simultaneously input to analogueconstant-current circuit 4-2 from signal processing circuit 2-1, andlow-voltage distribution switch drive signal Ihsel1 is also output.However, high voltage is not applied from the high voltage power sourceto the drive-side terminal of load ZL1 so the holding current cannotflow to the load side; also, a large load current resulting from theapplication of high voltage flows through means for detecting current10-1, so the output of an addition circuit that is arranged in the inputunit of analogue constant-current circuit 4-1 acts in the direction tocut off the output of analogue constant-current circuit 4-2, so thatthis output is not generated.

When a period Tp has elapsed, the high voltage switch drive signal andhigh voltage distribution switch drive signal disappear. DC--DCconverter circuit 1 is thereby isolated from the load. At this point,the large load current referred to above is still present in the load,so, due to the self-inductance characteristic of the load, the loadcurrent tries to maintain this value. However, the output of analogueconstant-current circuit 4-1 is cut off, so the current resulting fromthe inductance of the load is absorbed by the snubber circuit 16-1through the selected low-voltage distributive switching means 6-1. Theload current of inductive load ZL1 is decreased by the discharge ofenergy to snubber circuit 16-1, and the output of means for detectingcurrent 10-1 is also thereby decreased. When the load current ofinductive load ZL1 cuts in to a value matching the holding current valuesignal Ihref, analogue constant-current circuit 4-1 starts to supplycurrent.

The construction of analogue constant-current circuit 4 is shown in moredetail in FIG. 29.

Analogue constant-current circuit 4 comprises an adder 41 that adds theholding current value signal and the output of means for detectingcurrent 10 that detects the load current; an inverting amplifier 42 thatamplifies the result of this addition; an output transistor 45 thatoutputs current to the load from low-voltage power source 5 under thecontrol of the output of inverting amplifier 42; means for voltagedetection 44 that detects when the voltage drop generated across the twoterminals of this transistor 45 exceeds a prescribed value (in this casethe prescribed value is the voltage between base and emitter of abipolar transistor); and an output-disabling switch 43 that outputs theoutput of this means for voltage detection 44 to the outside only whenoutput transistor 45 is driven.

Now, when output current matching the holding current value signal Ihreffrom the analogue output circuit is supplied to the load, means forvoltage detection 44 is constantly monitoring the voltage drop generatedat both terminals of output transistor 45; if for example thetemperature of the load is low, causing its DC resistance to be small,the two-terminal voltage of the load becomes smaller than the outputvoltage of the low-voltage power source 5, with the result that thevoltage drop of output transistor 45 becomes large; thereupon, whenmeans for voltage detection 44 detects this, it outputs to low-voltagepower source 5 a voltage adjustment signal Vladj causing it to lower itsoutput voltage.

When low-voltage power source 5 receives this voltage adjustment signalVladj, it gradually lowers its output voltage. If there is no voltageadjustment signal Vladj, power source 5 has the function of graduallyincreasing its output. Consequently, the analogue constant-currentcircuit 4 supplies a constant current to the load and, due to the actionof means for voltage detection 44, control is effected such that theloss of the circuit is minimized.

When drive signal Sig terminates, the holding current value signal Ihrefbecomes 0 and the output of analogue constant-current circuit 4 isthereby cut off. Simultaneously, drive completion signal Irsel1 isoutput by signal processing circuit 2-1. Since the output of analogueconstant-current circuit 4-1 is then cut off, the surge voltagegenerated by the inductance component of the load is absorbed by snubbercircuit 16-1.

The operation of this circuit with respect to drive signal Sig1 wasdescribed above. However, in FIG. 26, respective drive signals Sig1 toSig4 are input independently of other drive signals Sig1 to Sig4, andthe respective circuits operate identically with respect to respectivedrive signals Sig1 to Sig4.

Next, the case where the respective drive signals are continuously inputas in FIG. 27 will be described. As shown in FIG. 23, DC--DC convertercircuit 1 and high voltage switching means 3 are common to four loadsZL1 to ZL4. However, closure of high-voltage switching means 3 andhigh-voltage distributive switching means 8-1 to 8-4 is restricted tothe period tp of FIG. 25 after input of respective drive signals Sig1 toSig4, and analogue constant-current circuits 4-1, 4-2 and snubbercircuits 16-1, 16-2 are respectively common to loads ZL1, ZL3 and loadsZL2, ZL4. Consequently, the same operation is obtained as in the casewhere drive signals Sig1 to Sig4 are independent, there being no circuitinterference between drive signals Sig1 and Sig2.

Also, even where there are mutually overlapping inputs as in FIG. 28,this circuit only performs operation as described above when the DC--DCconverter circuit 1 has completed accumulation of the prescribed highvoltage on its output capacitor by the respective drive commencementpoint at which high voltage is needed in the adjacent drive timing.

In the inductive load drive device described in the above embodiment,apart from the holding current of the load, in the initial drive period,a large current produced by application of high voltage flows in loadcurrent detecting means 10-1, 10-2 in the initial drive period. Forexample, if these load current detecting means 10-1, 10-2 are DCresistance means such as shunt resistors, this large currentinstantaneously generates a large amount of heat, which not onlyincreases the generation of heat of the circuit as a whole but alsoimpedes efficient utilization of the energy from DC--DC converter 1which is intended to be applied to the load. With the object ofameliorating this, there are provided bypass means 11-1, 11-2 inparallel with means for detecting current 10-1, 10-2, which arenon-conductive when the voltage across the terminals of these detectionmeans is below a prescribed voltage, but which have a constant-voltagecharacteristic such that they conduct, maintaining the voltage betweenthese two terminals, when a prescribed voltage is exceeded.

In this way, in the period of passage of the holding current, in whichthe value of the output voltage of means for detecting current 10-1,10-2 is valid, bypass means 11-1, 11-2 are non-conducting, but, at thecommencement of drive of inductive loads ZL1 to ZL4, whilst a largecurrent is passing due to application of high voltage to the load,bypass means 11-1, 11-2 conduct, so that the voltage across the twoterminals of means for detecting current 10-1, 10-2 is clamped at aprescribed voltage exceeding the output voltage produced by the holdingcurrent.

Consequently, whilst maintaining the function of cutting off the outputof the analogue constant-current circuit 4, excess generation of heatenergy by the means for detecting current can be prevented, therebyenabling the energy from the DC--DC converter 1 to be applied to theload more effectively.

Furthermore, in an inductive load drive circuit as described in theembodiments, conventionally, the surge current produced byself-induction of the load and generated when load drive was completedwas detected, and a load operation monitoring device was employed tomonitor normal termination of load operation. The monitor circuit 14shown in FIG. 23 is an improvement on such a load operation monitoringdevice. Details of this monitoring circuit 14 are shown in FIG. 30.

The principle of operation of this circuit is that, after lapse of atime tp shown in FIG. 25 after the supply of the large load current byapplication of high voltage from DC--DC converter 1 on drive of the loada large negative surge voltage is generated by cut-off of this largecurrent. A monitor circuit 14 inputs the terminal voltage of the loadthrough Zener elements 142-1 to 142-4 for selective detection ofnegative voltage. When generation of the surge voltage is thus detected,the monitor circuit actuates a one-shot circuit 141 to output a monitoroutput ACK.

Since this monitor output ACK is output at a time tp after input of thedrive signals, it has the advantage that the drive condition of the loadcan be detected at an earlier stage than in the case of the conventionalarrangement, in which this signal is output at the time point where loaddrive terminates.

Also, with the objective of preventing the surge of negative voltagegenerated by termination of drive of the load being confused with thesurge produced by cut-off of the large current, monitor circuit 14 inthe drive circuit shown in FIG. 23 is provided in combination withswitching means (mask switches) 144-1 to 144-4 that input the drivetermination signal and isolate the outputs of Zener elements 142-1 to142-4 for a fixed period after this input of the drive terminationsignal.

With such a construction, this monitor circuit 14 is able to monitor thedrive condition of the load at an early stage after input of the drivesignal of the load, and can prevent confusion with the time point oftermination of the load drive. Thus it can accurately output amonitoring signal even in the case where the drive timings of therespective loads overlap as shown in FIG. 27 and FIG. 28.

In the configuration shown in FIG. 23, a semiconductor switch istypically employed as switching means 3 to switch the high voltagegenerated by the DC--DC converter 1 on or off with respect to the load.However, when employing a semiconductor switch for so-called high sideswitching as shown in FIG. 23, difficulties are experienced in theselection of a semiconductor switch suited for industrial applications.For example, in the case of a junction transistor switch, the pnp typeof switch is suited to the construction of a high side switch, but, dueto the internal structure of a pnp type switch, a switch having thenecessary current characteristic and efficiency tends to be of largesize and high cost. Also, although there are many switches of the npntype that are suitable in respect of current characteristic andefficiency, due to the need to provide a higher voltage than the highvoltage generated by the DC--DC converter 1 in order to drive the baseof such an npn switch, they suffer from the drawback that the powersource for driving this base needs to have a certain level of currentcapacity.

In regard to this matter, a high voltage switch circuit employing avoltage drive element as in Japanese Patent Application No. H.6-098659is advocated, but if such circuits are employed in respect of a largenumber of loads the construction becomes too complicated. Circuitspossessing the property that, by inputting a trigger signal when thecircuit is closed, as in an SCR element, the element itself maintainsclosure if the subsequent load current is continued are also available.However, with such elements, although the closure circuit is simplifiedand losses during closure are adequately small, it is necessary toprovide a large amount of ancillary circuitry in order to open-circuit(extinguish) the element.

In the present invention, by using, as high voltage switching means 3, aswitch element employing a high voltage drive transistor element or thelike, that is capable of achieving cut off, and, by using as the meansfor distributing the output of this to a plurality of loads (highvoltage means for distribution 8), a trigger-driven type element such asan SCR element, by combining both of these, an SCR-element extinguishingcircuit is made unnecessary; furthermore, it becomes possible to sharesuch switch devices that are capable of achieving cut off with aplurality of loads, thereby greatly simplifying the circuitry andenabling costs to be reduced.

Also, in FIG. 23, regarding the distributive switching means 6 forconnecting the output of analogue constant-current circuit 4 indistributed fashion to the respective loads, when the output of DC--DCconverter 1 is applied to the loads, this high voltage output of DC--DCconverter 1 is applied to distributive switching means 6 in the oppositedirection. Since analogue constant-current circuit 4 that is connectedto the input of distributive switching means 6 is not designed to havehigh voltage applied to it in the opposite direction, as in the case ofthe output of an ordinary DC--DC converter 1, it was necessary toprovide a reverse current prevention means such as a diode in serieswith distributive switching means 6. In the present invention, byadopting as the distributive switching means 6 an element that itselfhas a reverse current blocking characteristic, such as an SCR element,the circuit can be simplified and loss can be reduced.

INDUSTRIAL APPLICABILITY

As described above, with the present invention, by adopting aconstruction in which the coil that is employed for charging thecapacitor in a DC--DC converter constituting the charging circuit of aninductive load drive device is a coil that is magnetized with greaterenergy density per unit area of the core by application of bias to thecore of the coil by using a permanent magnet or electromagnet, if thesame energy is to be obtained, this coil can be made of smaller size andlighter weight. Or, if a coil of the same size is to be employed, moreenergy can be obtained in a single switching cycle. Consequently, thecharger circuit can be made of smaller size, lighter weight, and higherefficiency and, as a result, the inductive load drive device itself canbe made of smaller size, lighter weight and higher efficiency.

Also, in the operation maintenance period of the inductive load, since,in contrast with the PWM system using conventional switching, the loadcurrent is controlled in analogue fashion, external radiation of noisecan be enormously reduced. Furthermore, this control can be combinedwith use of a low-voltage power source so, even though analogue controlis used, evolution of heat by the device can be kept to a very lowlevel.

Furthermore, by making the circuitry relating to the DC--DC converter,analogue constant-current circuit, and high voltage switching circuitcommon to a plurality of load circuits as far as respectively possible,an inductive load drive device can be provided that can be applied tomany kinds of applications without increasing the amount of circuitequipment.

We claim:
 1. A DC--DC converter circuit having a power source and a coilprovided with a magnetic core connected to the power source, in which aprocess that energy is accumulated on the magnetic core by applying thepower source voltage to the coil and the energy accumulated on themagnetic core is then discharged to a load, is performed repeatedly,characterized in that the magnetic core of the coil is magneticallybiased in a direction opposite to a direction of magnetization inducedby an electric current supplied from the power source so that themagnetic energy accumulated on the coil is increased.
 2. The DC--DCconverter circuit according to claim 1, comprising the power source, acoil having a magnetic core and connected to the power source, switchingmeans that opens and closes a closed circuit containing the power sourceand the coil, rectifying means whose one end is connected to theswitching means, for preventing reverse current, and a capacitorconnected in parallel with the switching means through the rectifyingmeans, in which energy is accumulated on the coil by applying a voltagefrom the power source to the coil by closing the switching means, andthe energy accumulated on the coil is accumulated on the capacitorthrough the rectifying means by opening the switching means with anarbitrarily determined timing and output, characterized in that themagnetic core of the coil is magnetically biased in a direction oppositeto a magnetic field induced by an electric current supplied from thepower source.
 3. The DC--DC converter circuit according to claim 2,wherein the magnetic core comprises a permanent magnet and the magneticcore is magnetically biased by a magnetic field generated by thepermanent magnet in a direction opposite to a direction of a magneticflux induced by the current supplied from the power source.
 4. TheDC--DC converter circuit according to claim 2, wherein the magnetic coreincludes a biasing winding and the magnetic core is magnetically biasedby supplying a desired current to the biasing winding from aconstant-current source, in a direction opposite to a magnetic fieldinduced by the current supplied from the power source.
 5. The DC--DCconverter circuit according to claim 1, comprising the power source, afirst coil having a magnetic core and connected to the power source;switching means that opens and closes a closed circuit including thepower source and the first coil; at least one second coil whose magneticcore is common with the first coil; rectifying means connected to oneend of the second coils, for preventing reverse current; and capacitorsrespectively connected in parallel with the at least one second coilthrough the rectifying means, wherein a voltage from the power source isapplied to the first coil by closing the switching means, causing energyto be accumulated on the magnetic core of the first coil, and the energyaccumulated on the magnetic core is accumulated on the respectivecapacitors by currents induced in the second coils through therectifying means when the switching means is opened with an arbitrarilydetermined timing, and is output, characterized in that the magneticcore is magnetically biased in a direction opposite to the magneticfield induced by an electric current supplied from the power sourcewhereby the magnetic energy accumulated on the first coil is increased.6. The DC--DC converter circuit according to claim 5, wherein themagnetic core comprises a permanent magnet, and the magnetic core isbiased magnetically a the magnetic field generated by the permanentmagnet in a direction opposite to the magnetic field induced by thecurrent supplied by the power source.
 7. The DC--DC converter circuitaccording to claim 5, wherein the magnetic core includes a biasingwinding and the magnetic core is magnetically biased by supplying adesired current to the biasing winding from a constant-current source,in a direction opposite to a magnetic field induced by the currentsupplied from the power source.
 8. The DC--DC converter circuitaccording to claim 1, comprising the power source, a coil connected tothe power source and having a magnetic core, switching means that opensand closes a closed circuit containing the power source and an entirewinding or a partial winding of the coil, rectifying means connected toone end of the entire winding or a partial winding of the coil, forpreventing reverse current, and a capacitor connected in parallel withthe entire winding or partial winding of the coil through the rectifyingmeans, wherein closure of the switching means applies the power sourcevoltage to the entire winding or partial winding of the coil, therebyaccumulating energy on the magnetic core of the coil, and wherein, byopening the switching means with an arbitrarily determined timing,energy accumulated on the magnetic core is accumulated on at least oneof the capacitors as electrical energy induced in the entire winding orpartial winding at least one location of the coil through the rectifyingmeans and is outputted, characterized in that the magnetic core ismagnetically biased in a direction opposite to the magnetic fieldinduced by the current supplied from the power source whereby themagnetic energy accumulated in the coil is increased.
 9. The DC--DCconverter circuit according to claim 8, wherein the magnetic corecomprises a permanent magnet, and the magnetic core is biasedmagnetically a the magnetic field generated by the permanent magnet in adirection opposite to the magnetic field induced by the current suppliedby the power source.
 10. The DC--DC converter circuit according to claim8, wherein the magnetic core includes a biasing winding and the magneticcore is magnetically biased by supplying a desired current to thebiasing winding from a constant-current source, in a direction oppositeto a magnetic field induced by the current supplied from the powersource.
 11. The DC--DC converter circuit according to claim 1,comprising the power source, a first coil connected to the power sourceand having a magnetic core, switching means that opens and closes aclosed circuit containing the power source and the first coil, firstrectifying means connected to at least one end of the switching means,for preventing reverse current, a first capacitor connected in parallelwith the switching means through the first rectifying means, a secondcoil connected to the first capacitor, second rectifying meanspreventing reverse current of the current flowing through the secondcoil, and a second capacitor connected to the second coil through thesecond rectifying means, wherein closure of the switching means appliespower source voltage to the first coil so that energy is accumulated onthe magnetic core of the coil and, by opening the switching means withan arbitrarily determined timing, the energy accumulated on the firstcoil is accumulated on the first capacitor through the first rectifyingmeans and the energy that is output from the first coil, including thecharge on the first capacitor is accumulated on the second capacitorthrough the second coil and second rectifying means and is output,characterized in that the magnetic core of the first coil ismagnetically biased in a direction opposite to a magnetic field inducedby an electric current supplied from the power source whereby themagnetic energy accumulated on the coil is increased.
 12. The DC--DCconverter circuit according to claim 11, wherein the magnetic core ofthe first coil comprises a permanent magnet, and the magnetic core ismagnetically biased by means of the magnetic field generated by thepermanent magnet in the opposite direction to the magnetic field inducedby the current supplied from the power source.
 13. The DC--DC convertercircuit according to claim 11, wherein the magnetic core of the firstcoil includes a biasing winding, and, by supplying a desired electriccurrent from a constant-current source to the biasing winding, themagnetic core is magnetically biased by means of the magnetic fieldgenerated by the winding in the opposite direction to the magnetic fieldinduced by the current supplied from the power source.
 14. The DC--DCconverter circuit according to claim 1, comprising the power source, afirst coil having a magnetic core and connected to the power source,switching means that opens and closes the closed circuit containing thepower source and the first coil, at least one second coil whose magneticcore is common to the first coil, first rectifying means connected toone end of the second coil, for preventing reverse current, firstcapacitors respectively connected in parallel with the second coilsthrough the first rectifying means, a third coil connected to at leastone of the first capacitors, second rectifying means that preventreverse current of the current flowing through the third coil, and athird capacitor connected to the third coil through the secondrectifying means, wherein, by closing the switching means, the powersource voltage is applied to the first coil, thereby accumulating energyon the magnetic core of the first coil; the energy accumulated on themagnetic core by opening the switching means with timing that may bedetermined arbitrarily is accumulated on the respective first capacitorsby means of the current induced in the second coil through the firstrectifying means; and energy output from the second coil including thecharge of the first capacitor is accumulated on the third capacitorthrough the third coil and second rectifying means, characterized inthat the magnetic core is magnetically biased in the direction oppositeto the magnetic field induced by the current supplied from the powersource whereby the magnetic energy accumulated on the first coil isincreased.
 15. The DC--DC converter circuit according to claim 14,wherein the magnetic core of the first coil comprises a permanentmagnet, and the magnetic core is magnetically biased by means of themagnetic field generated by the permanent magnet in the oppositedirection to the magnetic field induced by the current supplied from thepower source.
 16. The DC--DC converter circuit according to claim 14,wherein the magnetic core of the first coil includes a biasing winding,and, by supplying a desired electric current from a constant-currentsource to the biasing winding, the magnetic core is magnetically biasedby means of the magnetic field generated by the winding in the oppositedirection to the magnetic field induced by the current supplied from thepower source.
 17. A DC--DC converter circuit comprising the powersource, a first coil connected to the power source and having a magneticcore, switching means that opens and closes a closed circuit includingthe power source and an entire winding or a partial winding of the firstcoil, first rectifying means connected to one end of the entire windingor partial winding of the coil, for preventing reverse current, firstcapacitors connected in parallel with the entire winding or partialwinding of the coil through the first rectifying means, a second coilconnected to at least one of the first capacitors, second rectifyingmeans preventing reverse current of the current flowing through thesecond coil, and second capacitors connected to the second coil throughthe second rectifying means, wherein closure of the switching meansapplies the power source voltage to the entire winding or partialwinding of the coil, causing energy to be accumulated on the magneticcore of the coil, and wherein the energy accumulated on the magneticcore by opening of the switching means with an arbitrarily determinedtiming is accumulated on at least one of the first capacitors aselectrical energy induced in the entire winding or at least one locationof the partial winding of the first coil through the first rectifyingmeans, and the energy that is output from the first coil, including thecharge of the first capacitors, through the second coil and secondrectifying means, is accumulated on the second capacitors and output,characterized in that the magnetic core of the first coil ismagnetically biased in the opposite direction to the magnetic fieldinduced by the current supplied from the power source so that themagnetic energy accumulated on the first coil is increased.
 18. TheDC--DC converter circuit according to claim 17, wherein the magneticcore of the first coil comprises a permanent magnet, and the magneticcore is magnetically biased by means of the magnetic field generated bythe permanent magnet in the opposite direction to the magnetic fieldinduced by the current supplied from the power source.
 19. The DC--DCconverter circuit according to claim 17, wherein the magnetic core ofthe first coil includes a biasing winding, and, by supplying a desiredelectric current from a constant-current source to the biasing winding,the magnetic core is magnetically biased by means of the magnetic fieldgenerated by the winding in the opposite direction to the magnetic fieldinduced by the current supplied from the power source.
 20. An inductiveload drive device comprising a power source, a DC--DC converter circuitas set forth in claim 1 that generates a voltage higher than the powersource and is connected to the power source, and high voltage switchingmeans for applying to an inductive load the output of the DC--DCconverter circuit.
 21. An inductive load drive device comprising:a powersource, a DC--DC converter circuit according to claim 1 that isconnected to the power source and that generates a voltage higher thanthe power source voltage, high voltage switching means that switches onor off the output of the DC--DC converter circuit, a logical summationcircuit that is capable of driving the high voltage switching means inresponse to any of the at least one high voltage switch drive signalsinputted thereinto, at least one high voltage distributive switchingmeans for connecting the output of the high voltage switching means toat least one inductive load, a low voltage power source connected to thepower source and that outputs a variable output voltage at or below thepower source voltage, load current detecting means that detects loadcurrent flowing in the inductive load, at least one analogueconstant-current output circuit connected to the low voltage powersource, that inputs a holding current value signal and a load currentfeedback signal from the load current detecting means, and that controlsthe load current to a value matching the holding current value signal, alow voltage power source adjustment circuit that inputs the voltage dropamount of output means of the analogue constant-current output circuitand that generates a signal to lower the output voltage of the lowvoltage power source circuit if the voltage drop amount exceeds aprescribed value, at least one low voltage distributive switching meansfor connecting the output of the analogue constant-current outputcircuit to the at least one inductive load, at least one surgeabsorption means that absorbs the self-induction energy of the loadgenerated when the drive current of the at least one inductive load isreduced, and a signal processing circuit that inputs at least one loaddrive signal and, in respect of the respective load drive signals,during a prescribed fixed period from a time point signifying thecommencement of the load drive in question, outputs a high voltageswitch drive signal for driving the high voltage switching means and adrive signal of the high voltage distributive switching means forconnecting the output of the high voltage switching means to the loadthat is to be driven, which is determined by the load drive signal and,during a period for which the load drive signal that is input signifiescontinuance of load drive, outputs a prescribed holding current valuesignal to the analogue constant-current output circuit and,concurrently, outputs a drive signal of the low voltage distributiveswitching means for connecting the output of the analogueconstant-current output circuit to the load that is to be driven, whichis determined in accordance with the load drive signal.
 22. Theinductive load drive device according to claim 21, wherein the loadcurrent detecting means is a current detection resistor, and bypassmeans are provided in parallel with the current detection resistor andthat have a constant-voltage characteristic that is non-conductive whenthe voltage across both terminals of the current detection resistor isbelow a prescribed voltage and that conducts when the voltage acrossboth terminals of the current detection resistor exceeds the prescribedvoltage, whereby, when a current of more than the prescribed currentexceeding a current value matching the holding current value signalflows in the load to which the current detection resistor is connectedby the high voltage switching means and the high voltage distributiveswitching means, due to the voltage generated by the current at the twoterminals of the current detection resistor exceeding the prescribedvoltage of the bypass means, the load current is branched to the bypassmeans, thereby lowering the heat generated by the current detectionresistor.
 23. The inductive load drive device according to claim 21,wherein, for cases where, due to drive sequence of the inductive loads,drive times of the high voltage switching means do not overlap, theDC--DC converter circuit and the high voltage switching means are madecommon and, for cases where the periods for which drive of thecorresponding loads continues do not overlap, the analogueconstant-current output circuit and the load current detecting means aremade common.
 24. An inductive load drive device comprising a monitorcircuit that inputs the drive-side terminal voltage of an inductive loadand, when a drive current of the inductive load is cut off or rapidlydecreased, outputs an operation confirmation signal by detecting a surgecurrent generated by self-induction of the inductive load, wherein themonitor circuit outputs a confirmation signal that detects a surgeproduced when a large current flowing in the load due to high voltageapplied in an initial period of drive of the load is rapidly decreased,characterized in that, in order to prevent confusion of the surge with asurge produced when the load drive is terminated, the operatingconfirmation signal is masked by using a control signal indicative ofthe termination of drive of the inductive load.
 25. The inductive loaddrive device according to claim 21, wherein the high voltage switchingmeans comprises an element such as a transistor that is capable of beingcut-off in response to a control input, and the high voltagedistributive switching means comprises an element such as an SCR havinga self-holding function.
 26. The inductive load drive device accordingto claim 21, wherein the low voltage distributive switching meanscomprises an element having a self-holding function of conduction, suchas an SCR.
 27. A DC--DC converter circuit having a power source and acoil provided with a magnetic core connected to the power source, inwhich a process that energy is accumulated on the magnetic core byapplying the power source voltage to the coil and the energy accumulatedon the magnetic core is then discharged to a load, is performedrepeatedly, characterized in that the magnetic core of the coil ismagnetically biased in a direction opposite to a direction ofmagnetization induced by an electric current supplied from the powersource so that the magnetic energy accumulated on the coil isincreased,wherein the magnetic core comprises a permanent magnet and themagnetic core is magnetically biased by a magnetic field generated bythe permanent magnet in a direction opposite to a direction of amagnetic flux induced by the current supplied from the power source.